1. Field of the Invention
The present invention relates to a method of manufacturing optical disks using a stamper.
2. Description of the Prior Art
A method as shown in FIG. 1 is generally known as a method of manufacturing optical disks such as video disks.
According to the conventional method, a photoresist master disk, comprising a photoresist layer 2 formed on the main surface of a glass disk 1 as shown in FIG. 1A, is prepared, and a laser beam La which flickers according to a predetermined signal is irradiated onto the photoresist layer 2 to helically or concentrically form a latent image of a row of spots corresponding to predetermined information. Then, the exposed photoresist master disk is developed to create a row of minute bumps (hereafter referred to as "pits") corresponding to a signal to be recorded on the photoresist master disk, thus producing a developed master disk which has the pits-carrying photoresist layer 2 (information recording layer) and the glass disk 1 as shown in FIG. 1B. The photoresist layer 2 of the developed master disk is dried and fixed (post-baked) on the glass disk 1 to produce a dried master disk as shown in FIG. 1C. Then, silver is spattered on the photoresist layer 2 to form a silver conductive film 3 thereon, creating a mastering disk 3a having a multi-layered structure as shown in FIG. 1D. As described above, sputtering metal on a photoresist layer having pits renders a pits-carrying information recording face conductive. The produced mastering disk is immersed in a nickel electroforming tank to plate the silver conductive film 3 with nickel (Ni). As a result, a thick nickel layer 4 i.e., a nickel stamper is made, providing a disk as shown in FIG. 1E. The stamper or the nickel layer 4 is separated from the glass disk 1, as shown in FIG. 1F. The photoresist layer 2 and the silver conductive film 3 are removed from the stamper, yielding a nickel stamper shown in FIG. 1G.
Then, the nickel stamper is attached to a predetermined position of an injection molding apparatus. After the nickel stamper is closed, a melted transparent resin, such as flowable PMMA (polymethyl methacrylate) or PC (polycarbonate), is injected onto the stamper. After the resin is hardened, it is separated from the stamper, providing an optical disk replica having a face on which predetermined information is to be recorded.
The replica produced in this manner has a reflection film, such as an aluminum film, on its information recording face by a known method. Further, a protective film is coated on the reflection film, forming an optical disk. In general, two optical disks formed in this manner are bonded together and subjected to a finishing process, the resultant structure serving as a double-sided optical disk.
The preparation of a stamper, however, involves many electroforming steps, and the plating takes time, as described above. Further, an injection molding apparatus for manufacturing a replica is relatively large. Since it takes much time to manufacture a stamper by the conventional method, this method is not fully adequate for manufacturing recent optical disks which deal with multifarious types of audio visual software in a small quantity.